This invention relates to a pulley having a polymeric wheel molded around a metal bearing. In particular, it relates to the use of an elastomer in between the metal bearing and the polymeric wheel to prevent slippage therebetween.
In order to make pulleys lighter and less expensive, they are often made with a steel bearing surrounded by a polymeric wheel. While the pulley can be constructed so that the metal bearing snaps into place, many pulley manufacturers prefer a molded-in bearing because the polymeric wheel can be made to overlap the bearing and prevent it from dislodging. However, the coefficients of thermal expansion of the metal bearing and the polymeric wheel can differ and, when the pulley becomes hot, the polymeric wheel can expand and separate from the metal bearing. This results in slippage between the bearing and the wheel and failure of the pulley. While this problem can be overcome by using polymers that are more temperature stable, such as glass filled phenolics and nylons, they are more than twice as expensive as unfilled materials.